Electric arc furnaces



Oct. 30, 1962 C c. SHAW 3, 6 55 ELECTRIC ARC FURNACES Filed Nov. 12,1958 5 Sheets-Sheet 1 INVENTOR Caz/ am: .5710

Y M M ATTORNEY Oct..30, 1962 c. SHAW ELECTRIC ARC FURNACES 5Sheets-Sheet 3 Filed Nov. 12, 1958 IN VEN TOR (Zn-Tom Jaw BY Ham M M.

ATTORNEYS Oct. 30, 1962 c. SHAW 3,061,655

ELECTRIC ARC FURNACES Filed Nov. 12, 158 5 sheets-sheet 4 33 I II FIG. 6

FIG. 7

INVENTOR.

CLIFFORD SHAW i' MW Oct. 30, 1962 c. SHAW 3,061,655

ELECTRIC ARC FURNACES Filed Nov. 12, 1958 5 Sheets-Sheet 5 T- I t'' LMJFl G. 8

INVENTOR.

A T 1-0 RNEYJ United States Patent Ofifice 3,061,655 Patented Oct. 30,1962 3,061,655 ELECTRIQ ARC FURNACES Clifford Shaw, London, England,assignor to Shaw Process Development Corp, Port Washington, N.Y., acorporation of New York Filed Nov. 12, 1958, Ser. No. 773,350 9 Claims.(Cl. 1331) This invention relates to electric arc furnaces for meltingmetal for the purpose of making castings.

Electric arc furnaces for this purpose are known in which a crucible ismounted for rotation about a horizontal axis to enable melted metal tobe poured therefrom, the crucible being housed in a casing to which canbe secured the mould into which the charge of metal is to be poured, andthe casing and mould being rotatable with the crucible. It is sometimesessential that the melting and pouring of the metal shall take placeunder vacuum, and consequently the crucible casing, and a mould cover,have been arranged to form together a closed space from which air can beevacuated. Hitherto, however, the carbon rods between which the arc isformed have been mounted in stationary tubes about which the cruciblerotated, and, in order to maintain a vacuum in the enclosed space, ithas been necessary to provide glands around the tubes, and the provisionof glands which were satisfactory under the conditions existing has beena difficult problem.

The object of the present invention is to provide an improved electricarc furnace for the purpose described, which is free from many of thedisadvantages of the previously known furnaces.

According to the present invention, in an electric arc furnace includinga crucible mounted in a casing rotatable about a horizontal axis andhaving provision for the attachment thereto, in an airtight manner, of amould cover the carbon rods between which the arc is formed, andadjusting gear for the said carbon rods, are wholly enclosed inauxiliary casings forming a common enclosed space with the cruciblecasing and rotatable therewith.

Cooling means may be provided for preventing transmission of excessiveheat from the crucible to the auxiliary casings, said cooling meanscomprising coolant chambers surrounding the ends of the auxiliarycasings adjacent the crucible casing, and means for circulating a liquidcoolant through the said chambers.

The carbon rods may be mounted in travelling blocks slidable on guiderods to move the said rods in and out of the furnace, the rods extendingthrough bores in the said blocks and being clamped therein 'by wedgemembers mounted in tapered longitudinal grooves in the walls of the saidbores.

Cooling means may be provided in association with the adjusting gear forthe carbon rods, the guide rods conveniently being tubular and beingarranged in a circuit for cooling liquid.

The invention is hereinafter described with reference to theaccompanying drawings, in which:

FIGURE 1 is a front elevation of a form of arc furnace according to theinvention;

FIGURE 2 is a side elevation of the furnace shown in FIGURE 1;

FIGURE 3 is a partial sectional elevation, on an enlarged scale, on theline 33 of FIGURE 2;

FIGURE 4 is a sectional elevation on the line 4-4 of FIGURE 3;

FIGURE 5 is a sectional elevation of a detail;

FIGURE 6 is a fragmentary section side view of a modification of FIG. 3;

FIGURE 7 is a sectional plan view of FIGURE 6; and

FIGURE 8 is a rear elevation of the furnace showing a modification ofthe air withdrawal arrangement of FIGURE 2.

Referring to FIGURES 1 and 2 of the drawings, a cylindrical cruciblecasing 10 has secured thereto, at each end of a diameter thereofsubstantially at the middle of its length, a cylindrical sleeve 11. Tothe ends of the sleeves 11 remote from the crucible casing are secureddiscs 12 which extend radially outwardly beyond the sleeves 11, and restat their edges on pairs of rollers 13 mounted on a stand 14, so that thecrucible casing is 1'0- tatable about a horizontal axis passing throughthe centres of the discs. To each of the discs 12 there is detachablysecured an auxiliary casing 15 extending therefrom in the direction ofthe axis of rotation and having a radial extension 16 on one side. Eachof the auxiliary casings 15 encloses one of the carbon rods betweenwhich the arc is formed in the crucible, together with mechanism formoving the said carbon rod longitudinally, which mechanism will behereinafter described. A handwheel 17 at the outer end of each auxiliarycasing 15 is provided to operate the said mechanism.

One end of the crucible casing 10 is flanged externally at 18, and abell-shaped cover 19 is arranged for clamping to the said flange toenclose a mould 95, the mould being itself clamped to the cruciblecasing as hereinafter described. The other end of the crucible casing 10is permanently closed and is provided with a boss 20 formed with ascrew-threaded socket to receive the screw-threaded end of a rod 21carrying a counterweight 22 such that the Whole assembly issubstantially balanced about its axis of rotation. Each of the auxiliarycasings 15 is provided with a radially-extending handle 23 to facilitateturning of the assembly.

Referring now to FIGURE 3, the crucible 24 is enclosed in a block 25 ofinsulating refractory material which fits in the crucible casing 10 andlocates the crucible accurately therein, the crucible 24 and block .25being retained in the casing 10 by a plate 26 secured by screws 27(FIGURES 1 and 2) to the flange 18. The plate 26 is apertured to providea filling and pouring passage (not shown) and also a sighting passagealigned with a sighting aperture at 28 in the cover 19 and with theposition of the arc. Spaced inwardly from each sleeve 11 is a co-axialsleeve 29 which forms, with the said sleeve 11, the disc 12, and thewall of the crucible casing 10, an annular chamber 31 through whichcooling liquid is circulated by a pump and suitable conduits to reducethe transference of heat from the crucible casing 10 to the auxiliarycasings 15.

In each auxiliary casing 15 there are mounted a pair of parallel guiderods 3-2 (FIGURE 4), one of the guide rods being also shown in FIGURE 3.The rods 32 extend parallel to the axis about which the assembly isrotatable, and they support slidably a travelling block 33 (FIG- URES 3and 4) of generally triangular shape, the guide rods 32 passing throughthe block 33 adjacent two corners thereof. "Hie guide rods 32 areelectrically insulated from the auxiliary casingv 15 at both ends, forexample by bushes of insulating material. A screw-threaded rod 34 ismounted in the auxiliary casing 15 parallel to the guide rods 32, and isalso electrically insulated from the said casing, the rod 34 passingthrough a screw-threaded hole adjacent the third corner of the block 33.Each of the screw-threaded rods 34 has a plain portion 35 extendingthrough an opening in an end plate 36 closing the outer end of theauxiliary casing 15 in which that rod is mounted, and has one of thehandwheels 17 mounted on its outer end, with the interposition of aninsulating bush 37.

A packing 38 surrounding the plain portion 35 of the rod 34 is comprisedby a gland 39 of electrically insulating material tightened down on tothe packing 38 by nuts 41 engaging studs 42 passing through a metalplate 43 bearing on a shoulder on the gland.

The traveling block 33 is hollow, being formed by two substantiallytriangular plates 44, 44 between which are welded three metal bushes4'5, 46 and 47 (FIGURE 4) two of these bushes 45 and 46 providing theapertures for the guide rods 32, and the bush 47, which is internallyscrew-threaded, receiving the screw-threaded rod 34. A fourth bush 48extending between the plates 44, 44' substantially at their centres isadapted to receive the outer end of a carbon rod 49 which extendsthrough the crucible casing and through the wall of the crucible 24 intothe interior of the latter. A tapered longitudinal groove 51 is formedin the wall of the bore of the bush 48 to receive a tapered key 52adapted to grip the carbon rod 49 in the said bore. The key 52 is formedwith a radially outwardly projecting lug 53 at its thicker end, the lugbeing notched, and a screw 54, engaging in a screwthreaded hole in oneof the plates 44 of the block 33, is grooved circumferentially at 55.The groove 55 in the screw fits into the notch in the lug 53, so thatthe wedge can be moved in and out by rotating the screw 54.

The end plates 36 are formed with circular apertures 56 closed byscrew-caps 57 provided with packing rings 58 to ensure a substantiallyfluid-tight closure of the apertures 56. The caps 57, when removed,expose the ends of the carbon rods 49 and the heads of the screws 54, sothat the carbon rods can be readily removed, replaced and clamped inposition.

The space in the travelling blocks 33 between the plates 44, 44 isclosed by metal strips 59 welded in position, thus providing closedchambers in the said blocks to receive cooling liquid which absorbs andcarries away some of the heat from the carbon rods. The radialextensions 16 of the auxiliary casings are closed at their ends byplates 61 of electrically insulating material, each such plate 61 havingmounted in it two pipe connections 62, 62 from each of which a flexiblepipe 63 (FIGURE 3) leads to a further connection 64 on the travellingblock 33 in the corresponding casing 15. The connectors 62 are connectedexternally, by further flexible pipes 65 (FIGURE 2) to the pump alreadyreferred to which circulates cooling liquid through the chambers 31.There is also mounted in each plate 61 a binding post 66 from which aflexible conductor 67 preferably of metal braid, leads to the block 33,the binding posts 66 being connected to opposite poles of a source ofelectric current. The pipes 63 and the conductor 67, being flexible,allow of move 'ment of the block 33 along the guide rods 32.

In an alternative arrangement shown in FIGURES 6 i and 7, the block 33does not receive cooling liquid and is solid, the guide rods 32 beingtubular and connected to one another at their inner ends by a pipe 32a.One of the tubular rods 32 is connected at its outer end to a coolantsupply pipe 32b, the other being connected at its outer end to a returnpipe 32c the inner end of which communicate with a water jacket 32dsurrounding the carbon rod 34.-

To provide means for securing a mould to the crucible casing the plate26 has mounted on it, adjacent its periphery, two or more pillars, oneof which is shown at 68 in FIGURE 3, each of the pillars 68 carrying, atits end remote from the plate 26, a cylindrical head member 69 havingformedin it a series of axially spaced circumferential grooves. A dishedmetal plate 71 havinga diameter-such that its edge can engage in thegrooves in the head members 69 is notched at its edge in such positionsthat, by aligning the notches with the pillars, it can be insertedbetween the heads and then partially rotated to engage its edge with anyselected grooves in the heads. A flat metal plate 72, slidably mountedrelative to the dished plate 71 by means of a central stem 73 on theflat plate engagingin a sleeve 74 on the dished plate, is positioned onthe side of the latter nearer to the crucible casing, a coiledcompression spring 75 being mounted between the two plates 71 and 72 tourge them apart. A pair of pillars are fixed to the flat plate 72, oneon each side of the stem 73, one of the pillars being shown at 76 inFIGURE 3, the pillars 76 extending through openings in the dished plate71. A pivot pin 77 journalled in the pillars 76 has mounted on it a cam78 rotatable about the pivot pin by means of a handle 79, the contour ofthe cam 78 being such that if the handle 79 is turned to a position inwhich it is perpendicular to the plates 71 and 72 the spring 75 iscompressed and the flat plate 72 is drawn towards the dished plate 71,whereas movement of the handle 79 to a position in which it liesparallel to the plates 71, 72, as shown in FIGURE 3, allows the spring75 to extend.

A mould to receive metal to be melted in the crucible 24 can thus beclamped in position against the plate 26 by setting the cam 78 toretract the flat plate 72 relative to the dished plate 71, positioningthe dished plate 71 with its edge engaging in appropriate grooves in theheads 69 so that the flat plate 72 lies close to the bottom of themould, and moving the cam 78 to allow the flat plate 72 to engage thebottom of the mould. The mould 95 is formed with a filling orifice 95aregistering with the pouring passage 24a in the crucible. The dishedplate 71 serves as an adjustable reaction plate for the spring 75,whilst the plate 72 acts as a clamping plate for the mould.

The bell-shaped cover 19 has a relatively sharp edge 81 which rests on adeformable sealing ring 82 mounted in a rebate around the edge of theplate 26, and is held in position by clamp units 83 one of which isshown in detail in FIGURE 5. The clamp unit comprises a stud 84 carriedby a block 85 pivotally mounted in abracket 86 secured to the undersideof the flange 18, and a nut 87 on the stud, the cover 19 being providedwith slottted lugs 88 with which the studs 84 are engaged by turningthem about their pivots before the nuts 87 are tightened.

The depth of the cover 19 is such that, in any position of the dishedplate 71 relative to the grooved head members 69, the handle 79 isunable to move to the mouldreleasing position if the cover is on. Thecover 19 is provided with lifting handles 89.

The interior of the furnace is connected by a suitable conduit, such asthat shown at 9-1 in FIGURES 1 and 2, to an evaluator (not shown) sothat the interior of the furnace can be evacuated. The conduit 91 isshown as being connected to one of the auxiliary casings 15, but ifpreferred, the air may be withdrawn direct from the interior of thebell-shaped cover 19 through conduits extending upwardly through theflange 18 and plate 26. FIGURE 8 shows such an alternative arrangementfor withdrawing air from the interior of the furnace. According to thisarrangement the air is withdrawn direct from the interior of thebell-shaped cover 19' through conduits 93 extending upwardly throughplate 26, the pipes being connected by further pipes 94 to the evacuator(not shown). A vacuum gauge 92 is provided to indicate the pressure inthe furnace.

For loading, the furnace is positioned with the plate 26 at the top, thecounterweight 22 tending to hold it in that position. With thebell-shaped cover 19 removed, the crucible is charged, the mould beingthen placed in position and clamped, and the cover 19 being then clampedin position. The current is then switched on and the arc struck to beatand melt the charge. When the charge is melted, the whole assembly isinverted to cause the charge to flow into the mould.

The whole of the interior of the furnace is evacuated prior to themelting operation, and if a reducing atmosphere is required, a suitablegas is fed in after the air has been withdrawn.

The invention provides an electric arc furnace in which by arranging thewhole of the carbon rods within a space which can be evacuated, thenecessity for providing an airtight seal through which the said rods canslide is avoided, and adequate sealing of the evacuated space is morereadily and economically provided.

I claim:

1. A vacuum furnace for melting metal by an electric arc, said furnacecomprising a main casing, two closed auxiliary casings secured airtightto the main casing and radially extending from opposite side Wallsthereof; a crucible mounted within the main casing, a carbon rod mountedwith its entire length longitudinally slidable within each of saidauxiliary casings and extending from the respective casing through therespective main casing wall into the crucible, operating means forsliding said rods into and out of an are producing position in referenceto each other, a mold cover airtight attachable upon the top of saidmain casing, and support means supporting the main casing, the auxiliarycasings and the mold cover pivotal as a unit about a horizontal axis.

2. A furnace according to claim 1 and comprising cooling jacketssurrounding the auxiliary casing portions adjacent to the main casing,and means for circulating a coolant through said jackets to reduce thetransfer of heat from the crucible to the auxiliary casings.

3. A furnace according to claim 1 and comprising in each auxiliarycasing at least one guide rod mounted parallel with the respectivecarbon rod, and a travelling block slidable on the guide rod andreleasably keyed to the carbon rod for joint longitudinal displacementof the traveling block and the carbon rod along the guide rod, saidcarbon rod operating means being drivingly coupled with said travelingblocks for independently displacing the latter from the outside of theauxiliary casings.

4. A furnace according to claim 3 wherein said carbon rod operatingmeans comprises in each auxiliary casing a threaded rod rotatablymounted parallel to said carbon rod and said guide rod and threadedthrough the traveling block, and actuating means located outside eachauxiliary casing and coupled to the respective threaded rod for roratingthe same whereby the respective block and with it the respective carbonrod are correspondingly displaced within the auxiliary casing.

5. A furnace according to claim 3 wherein said guide rods are hollow andmeans are provided for circulating a coolant through said rods.

6. A furnace according to claim 1 and comprising cooling means disposedin close heat transferring relationship with said rod operating meansfor dissipating the heat transferred to said means from the rods.

7. A furnace according to claim 1 and comprising in each auxiliarycasing at least one guide rod mounted parallel with the respectivecarbon rod, and a hollow traveling block slidable on the guide rod andreleasably keyed to the carbon rod for joint longitudinal displacementof the traveling block and the carbon rod along the guide rod, saidcarbon rod operating means being drivingly coupled with said travelingblocks for independently displacing the same from the outside of theauxiliary casings, and further comprising means for circulating acoolant through said hollow traveling blocks.

8. A furnace according to claim 1 and comprising mold clamping means fordetachably securing a mold to the main casing, said clamping meansincluding upright pillars mounted on the main casing in circumferentialarrangement, a reaction plate engageable with said pillars in a selectedone of several positions of different spacings from the top of the maincasing, a clamping plate resiliently urged away from said reaction plateto exert clamping pressure upon a mold placed between the plate and thetop of the main casing, and means coacting with said clamping plate forpulling the same toward the reaction plate against said resilientaction.

9. A furnace according to claim 8 wherein said pillars mount headshaving longitudinally spaced circumferenial grooves, and wherein saidreaction plate has a diameter overlapping the heads of said pillars andis notched along its peripheral rim, the notches being circumferentiallyspaced to correspond with the circumferential spacing of said pillars.

References Cited in the file of this patent UNITED STATES PATENTS688,393 Contardo Dec. 10, 1901 949,511 Weeks Feb. 15, 1910 1,310,079Hechenbleickner July 15, 1919 1,926,573 Willcox Sept. 12, 1933

